The present invention relates generally to an improved method for preparing vascular replacements and/or arterial venous fistula, and particularly wherein a preformed umbilical cord is being utilized. More specifically, the method of the present invention relates to a technique for dehydrating and thereafter fixing the umbilical cord tissue into the desired preformed configuration. Implantable prosthetic devices for either permanent or semi-permanent implantation into the body for the controlled passage of fluids are in relatively wide usage throughout the world. Normally, such implantable devices are utilized for treating renal failure through dialysis, as well as for other disorders which require replacement of arteries or veins due to damaged vessels.
In order to achieve a proper implant, the material utilized must provide for a relatively sound surface seal, the seal properly controlling or preventing the passage of fluids therearound, and furthermore providing a seal which resists infection. It has been found that processed human umbilical cords are well suited for this purpose, since processed umbilical cords are normally not rejected by the host, and furthermore, are reasonably accepted by the subcutaneous tissues of the patient.
Normally, the human umbilical cord is a relatively straight tubular member, but is, of course, highly flexible. As in any flexible tubular structure of this type, bending or forming about a relatively small radius of curvature will cause kinking or buckling of the walls, with the kink resisting flow through the cord. In accordance with the present invention, however, the umbilical cords or segments thereof may be made to conform to a predetermined configuration including relatively sharp bends through a system of dehydration followed by fixing of the structure into the desired form.
Artificial dialysis has been widely used since its development by Kolff. Since the development and demonstration of this procedure, efforts have been undertaken to improve the techniques of gaining access to the blood stream of the patient, with access being required on an intermittent and sometimes frequent basis. In the past, bovine carotid arteries have been reasonably widely used for the cannulation of blood vessels in the arterial venous systems for hemodialysis. While bovine carotid arteries are usable for such applications, it has been determined recently that human umbilical cords are preferable for certain such applications.
In an article entitled "Possible Improvements in the Technique of Long Term Cannulation of Blood Vessels" by Quinton, Dillard, Cole and Scribner, Trans. Am. Soc. for Artif. Int. Organs, 7:60, 1960, an ideal cannula for blood vessels was described having the following features:
(1) The inner surface exposed to the body fluids should minimize clotting thereof; PA1 (2) The exterior surface should provide minimal tissue reaction so as to avoid rejection; PA1 (3) The exterior surface should permit bonding or attachment to the skin or subcutaneous tissue; PA1 (4) The skin should properly surround the cannula member for sealing; PA1 (5) The cannula material should be reasonably flexible in the tissue contacting area; PA1 (6) The cannula should be sufficiently durable so as to withstand trauma without permanent deformation; PA1 (7) The cannula should be sufficiently flexible so as not to occlude adjacent vessels; PA1 (8) The cannula should have a means to facilitate contact with various vessel sizes; PA1 (9) Means should be provided to permit attachment by clamping or the like to the external circuit means when required; and PA1 (10) The cannula should be arranged relatively close to the skin surface and not extend far into the subcutaneous tissue.
It has been found that human umbilical cords achieve most of these criteria, and are particularly well adapted to these criteria when treated in accordance with the technique of the present invention. Generally speaking, human umbilical cords, particularly when treated in accordance with the present invention, achieve a performance significantly superior to that of synthetic resinous materials, such as, for example, polyethylene terephthalate (Dacron) or the like.